Growth rate dependent impact of oscillating glucose conditions on Escherichia coli physiology: electronical supplement

Brand, Eva

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Growth rate dependent impact of oscillating glucose conditions on Escherichia coli physiology: electronical supplement

Brand, Eva

FG Bioverfahrenstechnik

Escherichia coli is the most used microorganism for biotechnological production processes due to its outstanding cultivation robustness and genetic and metabolic engineering possibilities. The established production process is a high cell density cultivation starting with a batch cultivation and followed by a fed-batch feeding strategy to avoid acetate accumulation and anaerobic conditions. The scale-up of a high cell density cultivation for increased productivity is accompanied with the appearance of heterogeneities in the cultivation broth especially regarding the substrate and oxygen distribution due to insufficient mixing when the cultivation mode changes from batch to fed-batch mode. These heterogeneities generally lead to a reduction in the specific production performance. To study the effect of heterogeneities on the Escherichia coli metabolism a scale-down reactor comprised of a stirred tank reactor in loop with a plug flow reactor was successfully established. The effect of heterogeneities, especially of oscillating glucose conditions, on the Escherichia coli metabolism are well studied for cultivations, where the cells are adapted to high glucose availability at batch phase and the growth rate decreases during transition to fed-batch strategy. In the present study the focus lies on the effect of oscillating glucose conditions on the Escherichia coli metabolism, when the cells are primarily adapted to low glucose availability and reduced growth rate. Therefore, a cultivation process was established with an internal, enzyme-based fed-batch before the start of oscillating glucose conditions (referred to as mechanical feeding). This cultivation process was compared in terms of cell growth, general cultivation parameters and accumulation of organic and amino acids to reference cultivation process without oscillating glucose conditions and to a cultivation with initial batch mode. Additionally, the proteome and selected transcriptome was analyzed for the newly established cultivation process and its reference cultivation. The growth rate and glucose availability before the onset of oscillating glucose conditions was found to have an immediate effect on the accumulation of organic acids and amino acids in the stirred tank of the scale-down reactor. Though organic acids accumulated along the plug flow reactor at oscillating glucose conditions for cells adapted to high and low growth rate, the re-assimilation was found to be reduced for the latter. 5 h of oscillating glucose conditions were not sufficient to synchronize the accumulation pattern of both cultivations. Proteome data show, that the increase in growth rate during transition from enzyme based fed-batch to mechanical fed-batch with oscillating glucose condition leads to a level decrease of protein involved in biosynthesis pathways. The increased growth rate caused more level changes of proteins of the central carbon metabolism and synthesis pathways for amino acids and nucleotide precursors than oscillating glucose conditions. In fact, the adaptation to oscillating glucose conditions for the newly established cultivation process compared to its reference stirred tank reactor cultivation on the proteome level was mainly found in the activation of the glyoxylate shunt and increase in two of four respiration complexes. This study shows, that the physiological status of the Escherichia coli cell before the change of cultivation parameter can have an important effect on its central metabolism and performance due to prolonged adaptation processes.

Oscillating glucose condition Escherichia coli physiology Proteome analysis Two-compartment reactor Scale-down Oszillierende Glukose Konzentration Escherichia coli Physiologie Proteom Analyse Zwei-Kompartimente Reaktor Verringerung der Skalierung

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